The world's finest single-malt whiskies come from the highland of Scotland. If the quality of the blended whisky derives from the quality of its component ingredients, then MacDuff's whisky must be the finest whisky in the world, because it blends no fewer than five Scotland's finest single-malt whiskies.
Premise 1: world's finest SINGLE-malt whiskies: let's say each has score: 8,8,9,9,9
Premise 2: Quality of blended whisky derives from quality of its component indredients: let's say f(M) = Quality of MacDuff's whisky.
Premise 3: MacDuff's whisky blends >= 5 finest Scotland's SINGLE-malt whishkies
Conclusion: MacDuff's whisky must be NO. 1 -> f(M) must be the highest score. The issue here is we don't know how to formulate the f(M) and that is what we are looking for in the answer.
The argument above could be seriously weaken if which of the followin were true?
A. The more single-malt whiskies involved in the batch of blended whisky, the finer the quality of whisky. -> we can't tell f(M) is the biggest number as we don't know how to formulate the f(M)
B. Whereas many of MacDuff's competitors have been in industry for decades or even century, the MacDuff brand was created within the last decade by marketing committee. -> no information related to the quality of the Blended whisky
C. Including more than five single-malt whiskies in a blended whisky is a waste, because no one can taste that many component flavors. -> it does means we don't need more than 5 ingredients but it doesn't provide information to judge wether the f(M) is the highest score
D. A blended whisky is as fine as the average quality of its components. -> f(M) = Average ( Ingredients) <= Max(Ingredients). Therefore, this answer weakens the conclusion
E. The concept of "finest" in a whisky is a subjective measure that cannot be quantified in a statistically valid way. -> provide no information to tackle the conclusion
IMO D